1. Technical Field
The present invention relates to palladium-based alloys and uses thereof. In particular, such alloys may be used in dental restorations, and more specifically, in dental implant restorations.
2. Background Information
It is well known that alloys to be used in the oral environment should provide a high degree of biocompatability and inertness to the conditions in the mouth. When these alloys are placed in electrical contact with metallic or other electrically conductive implants, it also becomes necessary to consider the possibility and potential results of galvanic coupling between dissimilar metals. The existence of a galvanic couple can cause the more anodic or active metal to corrode at an accelerated rate compared to the same material in an uncoupled situation. If an implant is made from titanium or titanium alloy, it is important to use an alloy for the superstructure that is at least as noble, or cathodic, as the titanium. Palladium base alloys achieve this level of nobility.
As with all alloys which may be used with dental porcelains, it is important to have a solidus temperature above 1100.degree. C. This allows sufficient temperature between the firing temperature of porcelain and the onset of melting of the alloy to allow soldering of the alloy. Additionally, to allow the alloy to be melted and cast with standard equipment in the dental laboratory the liquidus temperature should not exceed 1400.degree. C.
In order to obtain compatibility between the alloy and typical dental porcelains it is important for the alloy to exhibit a coefficient of thermal expansion between 13.9 and 15.2.times.10 .sup.-6 /C. This will result in the porcelain being placed into compression after firing which will impart the greatest strength to the ceramic veneering material.
Due to the difficulty of placing implants in the posterior region of the jaw, it is quite common in implant restorations for the superstructure to include a cantilever or unsupported extension posterior to the last abutment (see FIG. 1). If this section deforms excessively under the forces of mastication, the occlusal relationship between mandibular and maxillary arches will be altered in these regions. It is important, therefore, that the alloy used in the superstructure possess a rigidity that can withstand these masticatory forces.
Traditional gold-based alloys have been used for dental crown and bridge work for many years (see U.S. Pat. No. 3,574,611). Being electrochemically as noble as titanium, these alloys are suitable for use with titanium implants for an electrochemical standpoint. However, these alloys lack the strength and rigidity necessary to withstand the forces applied to cantilevered extensions. Newer palladium-based alloys have increased strength and rigidity over the gold-based alloys (see, e.g., U.S. Pat. No. 3,819,366 and U.S Pat. No. 4,400,350). However, in long span cantilever sections, even they may not possess sufficient rigidity to resist masticatory forces.
It is therefore an object of the present invention to provide a novel palladium alloy which meets all of the requirements for conventional crown and bridge fabrication as well as an alloy that possesses increased rigidity to provide support in cantilevered designs.